Royal Spa hot tub is working but display wont show temperature reading anymore only "Spb"???

looks like it's got a bad thermister or thermostat
E03 The pump's thermometer reads the water temperature below 4°C (40°F)
1. The water temperature is lower than 4°C (40°F).1. The spa is not designed to operate with water temperatures lower than 4?C (40°F). Please unplug the pump and move to a warmer ambient temperature. The pump should only be restarted when the water temperature reaches 6°C (43°F).

» 2. The pump's thermometer is broken.
Hot Tub Ireland

Julie Palmer... hello,

Somewhere you got a THERMOSTAT that is giving a bogus reading (on a fairly nominal temperature)...

You are going to have to find it... and most likely replace it.

https://www.bing.com/search?q=hot+tub+thermostat&form=EDGEAR&qs=PF&cvid=6bf0d109ca4a4c49b09ff562b296ea64&pq=hot%20tub%20thermostat&PC=DCTE

didnt specify if you had a 4 8 or 10 button panel your unit is locked the only control that will work is temperature your owners manual has how to unlock it under side panel the following link is for an 8 button panel and the instructions are on page 6
http://qcaspas.com/media/pdf/Jewelp3-8Btn.pdf

all systems must be working or the spa will not heat. If one of the sensors is not functioning then the spa water will not heat.

Rod
US Parts Center

If a floating thermometer is more than 3-4 Degrees F off what the control panel display temperature then the temperature sensor has likely failed.

This indicates a sensor failure. Either the temperature sensor has failed, or it has become disconnected from the control unit. If you find that it is still in place, replace the sensor.

"OH" is an overheat error. In normal function, it is used as a safety shut off if the spa water temperature reaches over 110 degrees in the event of a thermostat failure. But more commonly, (if the water temp hasn't gotten too hot) it indicates that the temp sensor(s) have failed. If you have a digital display on the topside controller of your spa, then it is a circuit board controlled spa pack. Most spa builders use the same control pack manufacturer - Balboa Watergroup. The sensor kit usually consists of 2 probes and wires that plug directly onto the circuit board. Depending on the spa, they could both be located onto the heater manifold, or one on the manifold and one mounted to the tub making direct contact with the water via a thru-wall sensor mount. If I knew the spa manufacturer, I could further assist you. If you replace the sensors, and encounter the same problem... then the circuit board is bad, and usually a costly replacement. The sensors are usually listed as a "BA sensor assy" Hope this helps you,

Your temperature control is way out of calibration or, it's wired wrong. Remove it and check it in a glass of water. Use an ohm meter across the heater wires. As you add hot wwater, the heater contacts should open.